Mice normally run along the perimeter of the rooms and not in the middle of the floor, if they are house familiar. Sadie, you might have a little mouse that came into the house for the first time and is disoriented. It's kinda cute and then when it's used to the house, it'll start running on the floor right up along side of the walls.
Once it settles in you might not see it again until it mates and has babies. At that point you'll begin to see little hide away places where they shit and urinate. In some ways they are a lot like hamsters, who will only perform elimination in designated areas - away from the nests.
As cute as it is, I'd nail the little fucker now before that place turns into Mouse Hotel.
